Improvement of microstructural and optical properties of GaN layer on sapphire by nanoscale lateral epitaxial overgrowth

Nanoscale lateral epitaxial overgrown (NLEO) GaN layers were investigated for the improvement of microstructural and optical properties of GaN. Nanoporous SiO2 films on the surfaces of GaN/sapphire (0001) were fabricated by inductively coupled plasma etching using anodic alumina templates as etch masks, resulting in an average pore diameter and interpore distance of 60 and 110nm, respectively. GaN was grown over the nanoporous SiO2 layer using metal organic chemical vapor deposition to realize a continuous and smooth film. NLEO GaN was found to result in a significant reduction of threading dislocation density as characterized by transmission electron microscopy and atomic force microscopy. The threading dislocation density was ∼107cm−2 at the surface of NLEO GaN. The narrower band-edge excitonic transition in photoluminescence spectrum shows a better optical quality in the NLEO GaN film.